Electrodynamic loudspeaker



Patented Oct. 25, 1938 UNITED STATES PATENT OFFICE 2,134,064ELECTRODYNAMIC LOUDSPEAKER Friedrich Ulrich,

Berlin- Siemensstadt,

and

Application May 26, 1938, Serial No. 81,796 In Germany June 5, 1935 4Claims.

This invention is concerned with loudspeakers of the electro-dynamic ormoving coil type, and more particularly to the magnet system of suchloudspeakers.

5 Heretofore it has not been possible, in electrodynamic loudspeakers,to completely transform the energy used for excitation into magneticfield intensity in the air gap. A considerable portion of the magneticflux is lost due to straying when the electro-magnets are of cup-shape.Although attempts have been made in reducing the air gap as much aspossible, an essential improvement of the degree of efiiciency could notbe attained.

A considerable advance is made by the present invention according towhich in magnet systems for electro-dynamic loud speakers, two exciteror field windings are provided having a common magnetic path and whichare arranged at such a distance from each other that a magnetic field oof high density is produced therebetween and in which a conductoroscillates. The conductor has passed through it voice currents and isconnected to a sound radiator or diaphragm. The magnetic system on theone hand can be so constructed that the two exciter or field windingshave the same magnetic axis and excitation is carried out in the samesense so that the air gap containing the conductor passed by voicecurrents can be arranged laterally to the magnetic axis. On the otherhand, the exciter windings having the same magnetic axis, may be excitedin the opposite sense so that the resultant fiux will be the greatestbetween the opposite faces of the windings. Consequently in thisconstruction a the air gap is placed in this part of the field, i. e.,

parallel to the magnetic axis. Especially in this construction themagnetic flux produced by the exciter winding is compelled to take itscourse through the air gap extending between the two 0 exciter windingsover the entire length of the annular core. Losses through strayingeffects are thus avoided in the present arrangement to the greatestextent thus obtaining an essentially higher degree of efllciency than inprior arrangements.

Further particulars of the invention will be explained in connectionwith the accompanying drawing wherein, by way of example, severalembodiments are represented in Figures 1 to 3.

In Figure 1, item I designates an annular core of soft iron havingchannel-like passages 2 and 3 arranged in succession in the direction ofthe axis and serving for accommodation of the exciter or field windings4 and 5. Between the two passages an annular slot 6 is provided in whichthe winding 1 passed by speech currents is placed. The speech coil whichmay be mounted on a coil body of small wall thickness has connectionstrips 8 attached thereto brought outside through openings 9 in themagnet core, and which may be joined to a membrane, such as a conicaldiaphragm for instance. These strips may at the same time also beutilized as lead-ins for the oscillatory voice coil. As seen from thefigure the connection strips also cross the exciter winding 4, forinstance at H).

As already pointed out, the two windings producing the field are excitedin the opposite sense as indicated in the figure by the arrows I I andI2. In this way there is produced between the two coils in the magnetcore, a course of the field extending in the same direction and having ahigh density. Obviously, in the arrangement shown, there is no occasionfor the field to form stray field lines so that approximately the entireenergy used for excitation will be consumed for the production of asufficiently high field intensity in the air gap 6 whereby in thepresent arrangement a high efiiciency is obtained.

Figure 2 shows a practical example of an embodiment of the newprinciple. Obviously in the construction according to Figure 1difficulties would be encountered in inserting the exciter windings aswell as the oscillatory coil in the magnet core. In the constructionaccording to Figure 2, a way is shown by which these difllculties areavoided. The magnet core in this case consists of an annular part [3 ofE-shaped cross section whereby two recesses l4 and ii for placing theexciter windings l8 and Il are formed. Towards the outside these groovesare closed by means of cylinder l8 of soft iron placed over the core. Asindicated in the figure the central rim of the E-shaped cross section issomewhat shorter than the outer rims thereby leaving an annular gapbetween the center rim and the cylinder for accommodating the voice coil2|. In the core I3 and preferably also in the exciter winding l6 groovesl9 and 20 are provided through which the connections between the voicecoil and a conical diaphragm 22 are passed. These connections may at thesame time be used as lead-ins for the oscillatory coil. In order toinsert the lead-ins for the exciter windings, channels are preferablyprovided in core [3. Otherwise the functioning of the magnet systemcompletely corresponds to that explained in connection with Figure 1.

Figure 3 finally shows a modification of the embodiment according toFigure 2, in which the the oscillatory coil 28 which may be connected tothe diaphragm by means of connections 29. Also in this case openings 3|are provided for passing the connections through the magnet core 25 andthrough the exciterwindi'ng 30.

What we claim is: 1 1. An electro-dynamic loudspeaker comprising acylindrical core of magnetic material, a' pair of spaced coaxiallydisposed field windings arranged within said core, said core having anannular air gap in the space between the field windings, a voice coilarranged within said air gap, a vibratile diaphragm, and connectorsjoined between the ,voice coil and the diaphragm, certain of saidconnectors serving as the lead-in conductors for the .voice, coil. 7

2. An electro-dynamic loudspeaker according to claim 1 wherein the fieldwindings and the Voice coil are disposed in channels formed on the outersurface of the magnetic core and a soft iron cylinder fitted over theoutside of the core.

3. An electro-dynamic loudspeaker according to claim 1 wherein the-fieldwindings and the voice coil are disposed in channels formed on the innersurface of the magnetic core and a soft iron cylinder fitted within thecore.

4; An electro-dynamic loudspeaker magnetic system, comprising an annularcore member, a pair 'of similarly shaped field windings, spaced apartcoaxially and embedded in said core member, and an annular air gap foraccommodating a movable voice coil formed in said core member andcoaxially positioned between the field wind- .ings, the directions ofthe magnetic fields prouced by said windings within the air gap being inthe same direction whereby a magnetic field of high density is producedtherein.

Q FRIEDRICH ULRICH. ALEXANDER VSCI-IAAF.

